1. Field of the Invention
This invention relates generally to a syringe for the controlled discharge of viscous materials, and, more particularly to a syringe for the controlled discharge of dental materials.
2. Description of the Prior Art
A syringe of the prior art is described, for example, in the product information published by Heraeus Kulzer GmbH "Charisma-Inlays--Gewinn durch Perfektion und Asthetik" [Charisma Inlays--Profit from Perfection and Appearance] (31292/D 125 sK dt./WPR 12 12 200). These syringes, which contain the viscous dental materials sold under the name "Charisma" (Charisma is a registered trademark of Heraeus Kulzer GmbH), have a cartridge filled with dental material. This cartridge has a tapered outer circumference on its discharge end, on which a cap is placed. In the end of the cartridge opposite the discharge end, a rotary piston is inserted which is in contact on one end with a sleeve-shaped stopper which, in turn, is in contact with the viscous material in the cartridge. The rotary piston is provided with a threaded portion which is guided in a bearing which is in the form of a nut. This nut is an approximately rectangular plate which has a central threaded opening. This nut is inserted into a slot in the insertion end of the cartridge, so that it is secured, with respect to the rotary piston screwed into the threaded hole, against rotation relative to the cartridge. To discharge the dental materials from the cartridge, the cap is removed from the cartridge and the rotary piston, which has a handle on its end, is twisted into the cartridge and the stopper is pushed toward the discharge end of the cartridge. To depressurize the stopper, which applies pressure to the material when the syringe is not being used, the rotary piston is twisted out of the cartridge in the opposite direction of rotation.
The syringes described above have been used successfully for years. But it has been found in handling the syringes that for very different materials, in particular materials which differ in terms of their viscosity and the amount of material to be discharged, that different advance speeds of the threaded rods may be required. This can be accomplished on one hand by means of the speed of rotation with which the rotary piston in the bearing advances as a result of its rotation or, on the other hand, the manufacturer can provide pistons with threads of different pitches which are rotated in corresponding bearing parts to achieve different advance speeds and rates of discharge.
Additional syringes for the discharge of viscous materials are disclosed, for example, in U.S. Pat. No. 3,581,399, German Application No. 42 00 044 A1, German GM 78 37 177 and U.S. Pat. No. 3,900,954. Each of these syringes and syringe system has specific features and characteristics. U.S. Pat. No. 3,581,399 discloses a syringe which has interchangeable tips or nozzles which, for example, are curved in the shape of a thin channel for controlled application of dental material to one spot on a tooth to be worked on. German Application No. 42 00 044 A1 discloses a dental cartridge for the discharge of a multi-component material for dental fillings which is inserted in a syringe controlled by a lever. This syringe has a pistol-like adapter into which the cartridge containing the dental material is inserted. German GM 78 37 177 discloses a syringe for the direct application of dental filling material in which the container which holds the filling material is designed as a collapsible capsule inserted into the cartridge. U.S. Pat. No. 3,900,954 discloses a syringe which is similar to the syringe disclosed in U.S. Pat. No. 3,581,399. A piston which has a projecting tip is inserted under some friction into a cartridge and the tip of the piston presses into a sleeve-shaped part in which the dental material is located. The small, sleeve-shaped part is attached to an end of the cartridge and simultaneously forms the discharge tip or nozzle for the material.
An object of the present invention is to provide a syringe for the discharge of a measured amount of viscous materials, in particular dental materials, which facilitates both the discharge of the viscous material from the syringe and the assembly or filling of the syringe by the manufacturer.